Blender python math operations on vertex
When you initialize total_points outside the loop it should work

import mathutils
..
..
total_points = mathutils.Vector((0,0,0))

for vert in verts_in_face:
    local_point = current_obj.data.vertices[vert].co
    total_points = total_points + local_point


For all available vector operations you can lookup the mathutils docs